1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2003 Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
25 ------------------------------------------------------------------------------
27 -- This package contains various subprograms involved in compile time
28 -- evaluation of expressions and checks for staticness of expressions
29 -- and types. It also contains the circuitry for checking for violations
30 -- of pure and preelaborated conditions (this naturally goes here, since
31 -- these rules involve consideration of staticness).
33 -- Note: the static evaluation for attributes is found in Sem_Attr even
34 -- though logically it belongs here. We have done this so that it is easier
35 -- to add new attributes to GNAT.
37 with Types; use Types;
38 with Uintp; use Uintp;
39 with Urealp; use Urealp;
43 ------------------------------------
44 -- Handling of Static Expressions --
45 ------------------------------------
47 -- This package contains a set of routine that process individual
48 -- subexpression nodes with the objective of folding (precomputing)
49 -- the value of static expressions that are known at compile time and
50 -- properly computing the setting of two flags that appear in every
51 -- subexpression node:
53 -- Is_Static_Expression
55 -- This flag is set on any expression that is static according
56 -- to the rules in (RM 4.9(3-32)).
58 -- Raises_Constraint_Error
60 -- This flag indicatest that it is known at compile time that the
61 -- evaluation of an expression raises constraint error. If the
62 -- expression is static, and this flag is off, then it is also known
63 -- at compile time that the expression does not raise constraint error
64 -- (i.e. the flag is accurate for static expressions, and conservative
65 -- for non-static expressions.
67 -- If a static expression does not raise constraint error, then the
68 -- Raises_Constraint_Error flag is off, and the expression must be
69 -- computed at compile time, which means that it has the form of either
70 -- a literal, or a constant that is itself (recursively) either a literal
73 -- The above rules must be followed exactly in order for legality
74 -- checks to be accurate. For subexpressions that are not static
75 -- according to the RM definition, they are sometimes folded anyway,
76 -- but of course in this case Is_Static_Expression is not set.
78 -------------------------------
79 -- Compile-Time Known Values --
80 -------------------------------
82 -- For most legality checking purposes the flag Is_Static_Expression
83 -- defined in Sinfo should be used. This package also provides
84 -- a routine called Is_OK_Static_Expression which in addition of
85 -- checking that an expression is static in the RM 4.9 sense, it
86 -- checks that the expression does not raise constraint error. In
87 -- fact for certain legality checks not only do we need to ascertain
88 -- that the expression is static, but we must also ensure that it
89 -- does not raise constraint error.
91 -- Neither of Is_Static_Expression and Is_OK_Static_Expression should
92 -- be used for compile time evaluation purposes. In fact certain
93 -- expression whose value is known at compile time are not static
94 -- in the RM 4.9 sense. A typical example is:
96 -- C : constant Integer := Record_Type'Size;
98 -- The expression 'C' is not static in the technical RM sense, but for
99 -- many simple record types, the size is in fact known at compile time.
100 -- When we are trying to perform compile time constant folding (for
101 -- instance for expressions such as 'C + 1', Is_Static_Expression or
102 -- Is_OK_Static_Expression are not the right functions to test to see
103 -- if folding is possible. Instead, we use Compile_Time_Know_Value.
104 -- All static expressions that do not raise constraint error (i.e.
105 -- those for which Is_OK_Static_Expression is true) are known at
106 -- compile time, but as shown by the above example, there are cases
107 -- of non-static expressions which are known at compile time.
113 procedure Check_Non_Static_Context (N : Node_Id);
114 -- Deals with the special check required for a static expression that
115 -- appears in a non-static context, i.e. is not part of a larger static
116 -- expression (see RM 4.9(35)), i.e. the value of the expression must be
117 -- within the base range of the base type of its expected type. A check
118 -- is also made for expressions that are inside the base range, but
119 -- outside the range of the expected subtype (this is a warning message
120 -- rather than an illegality).
122 -- Note: most cases of non-static context checks are handled within
123 -- Sem_Eval itself, including all cases of expressions at the outer
124 -- level (i.e. those that are not a subexpression). Currently the only
125 -- outside customer for this procedure is Sem_Attr (because Eval_Attribute
126 -- is there). There is also one special case arising from ranges (see body
127 -- of Resolve_Range).
129 procedure Check_String_Literal_Length (N : Node_Id; Ttype : Entity_Id);
130 -- N is either a string literal, or a constraint error node. In the latter
131 -- case, the situation is already dealt with, and the call has no effect.
132 -- In the former case, if the target type, Ttyp is constrained, then a
133 -- check is made to see if the string literal is of appropriate length.
135 type Compare_Result is (LT, LE, EQ, GT, GE, NE, Unknown);
136 subtype Compare_GE is Compare_Result range EQ .. GE;
137 subtype Compare_LE is Compare_Result range LT .. EQ;
138 function Compile_Time_Compare
140 Rec : Boolean := False)
141 return Compare_Result;
142 -- Given two expression nodes, finds out whether it can be determined
143 -- at compile time how the runtime values will compare. An Unknown
144 -- result means that the result of a comparison cannot be determined at
145 -- compile time, otherwise the returned result indicates the known result
146 -- of the comparison, given as tightly as possible (i.e. EQ or LT is a
147 -- preferred returned value to LE). Rec is a parameter that is set True
148 -- for a recursive call from within Compile_Time_Compare to avoid some
149 -- infinite recursion cases. It should never be set by a client.
151 procedure Flag_Non_Static_Expr (Msg : String; Expr : Node_Id);
152 -- This procedure is called after it has been determined that Expr is
153 -- not static when it is required to be. Msg is the text of a message
154 -- that explains the error. This procedure checks if an error is already
155 -- posted on Expr, if so, it does nothing unless All_Errors_Mode is set
156 -- in which case this flag is ignored. Otherwise the given message is
157 -- posted using Error_Msg_F, and then Why_Not_Static is called on
158 -- Expr to generate additional messages. The string given as Msg
159 -- should end with ! to make it an unconditional message, to ensure
160 -- that if it is posted, the entire set of messages is all posted.
162 function Is_OK_Static_Expression (N : Node_Id) return Boolean;
163 -- An OK static expression is one that is static in the RM definition
164 -- sense and which does not raise constraint error. For most legality
165 -- checking purposes you should use Is_Static_Expression. For those
166 -- legality checks where the expression N should not raise constaint
167 -- error use this routine. This routine is *not* to be used in contexts
168 -- where the test is for compile time evaluation purposes. Use routine
169 -- Compile_Time_Known_Value instead (see section on "Compile-Time Known
172 function Is_Static_Range (N : Node_Id) return Boolean;
173 -- Determine if range is static, as defined in RM 4.9(26). The only
174 -- allowed argument is an N_Range node (but note that the semantic
175 -- analysis of equivalent range attribute references already turned
176 -- them into the equivalent range).
178 function Is_OK_Static_Range (N : Node_Id) return Boolean;
179 -- Like Is_Static_Range, but also makes sure that the bounds of the
180 -- range are compile-time evaluable (i.e. do not raise constraint error).
181 -- A result of true means that the bounds are compile time evaluable.
182 -- A result of false means they are not (either because the range is
183 -- not static, or because one or the other bound raises CE).
185 function Is_Static_Subtype (Typ : Entity_Id) return Boolean;
186 -- Determines whether a subtype fits the definition of an Ada static
187 -- subtype as given in (RM 4.9(26)).
189 function Is_OK_Static_Subtype (Typ : Entity_Id) return Boolean;
190 -- Like Is_Static_Subtype but also makes sure that the bounds of the
191 -- subtype are compile-time evaluable (i.e. do not raise constraint
192 -- error). A result of true means that the bounds are compile time
193 -- evaluable. A result of false means they are not (either because the
194 -- range is not static, or because one or the other bound raises CE).
196 function Subtypes_Statically_Compatible
200 -- Returns true if the subtypes are unconstrained or the constraint on
201 -- on T1 is statically compatible with T2 (as defined by 4.9.1(4)).
202 -- Otherwise returns false.
204 function Subtypes_Statically_Match (T1, T2 : Entity_Id) return Boolean;
205 -- Determine whether two types T1, T2, which have the same base type,
206 -- are statically matching subtypes (RM 4.9.1(1-2)).
208 function Compile_Time_Known_Value (Op : Node_Id) return Boolean;
209 -- Returns true if Op is an expression not raising constraint error
210 -- whose value is known at compile time. This is true if Op is a static
211 -- expression, but can also be true for expressions which are
212 -- technically non-static but which are in fact known at compile time,
213 -- such as the static lower bound of a non-static range or the value
214 -- of a constant object whose initial value is static. Note that this
215 -- routine is defended against unanalyzed expressions. Such expressions
216 -- will not cause a blowup, they may cause pessimistic (i.e. False)
217 -- results to be returned.
219 function Compile_Time_Known_Value_Or_Aggr (Op : Node_Id) return Boolean;
220 -- Similar to Compile_Time_Known_Value, but also returns True if the
221 -- value is a compile time known aggregate, i.e. an aggregate all of
222 -- whose constituent expressions are either compile time known values
223 -- or compile time known aggregates.
225 function Expr_Value (N : Node_Id) return Uint;
226 -- Returns the folded value of the expression N. This function is called
227 -- in instances where it has already been determined that the expression
228 -- is static or its value is known at compile time (ie the call to
229 -- Compile_Time_Known_Value (N) returns True). This version is used for
230 -- integer values, and enumeration or character literals. In the latter
231 -- two cases, the value returned is the Pos value in the relevant
232 -- enumeration type. It can also be used for fixed-point values, in
233 -- which case it returns the corresponding integer value. It cannot be
234 -- used for floating-point values.
236 function Expr_Value_E (N : Node_Id) return Entity_Id;
237 -- Returns the folded value of the expression. This function is called
238 -- in instances where it has already been determined that the expression
239 -- is static or its value known at compile time. This version is used
240 -- for enumeration types and returns the corresponding enumeration
243 function Expr_Value_R (N : Node_Id) return Ureal;
244 -- Returns the folded value of the expression. This function is called
245 -- in instances where it has already been determined that the expression
246 -- is static or its value known at compile time. This version is used
247 -- for real values (including both the floating-point and fixed-point
248 -- cases). In the case of a fixed-point type, the real value is returned
249 -- (cf above version returning Uint).
251 function Expr_Value_S (N : Node_Id) return Node_Id;
252 -- Returns the folded value of the expression. This function is called
253 -- in instances where it has already been determined that the expression
254 -- is static or its value is known at compile time. This version is used
255 -- for string types and returns the corresponding N_String_Literal node.
257 function Expr_Rep_Value (N : Node_Id) return Uint;
258 -- This is identical to Expr_Value, except in the case of enumeration
259 -- literals of types for which an enumeration representation clause has
260 -- been given, in which case it returns the representation value rather
261 -- than the pos value. This is the value that is needed for generating
262 -- code sequences, while the Expr_Value value is appropriate for compile
263 -- time constraint errors or getting the logical value. Note that this
264 -- function does NOT concern itself with biased values, if the caller
265 -- needs a properly biased value, the subtraction of the bias must be
266 -- handled explicitly.
268 procedure Eval_Actual (N : Node_Id);
269 procedure Eval_Allocator (N : Node_Id);
270 procedure Eval_Arithmetic_Op (N : Node_Id);
271 procedure Eval_Character_Literal (N : Node_Id);
272 procedure Eval_Concatenation (N : Node_Id);
273 procedure Eval_Conditional_Expression (N : Node_Id);
274 procedure Eval_Entity_Name (N : Node_Id);
275 procedure Eval_Indexed_Component (N : Node_Id);
276 procedure Eval_Integer_Literal (N : Node_Id);
277 procedure Eval_Logical_Op (N : Node_Id);
278 procedure Eval_Membership_Op (N : Node_Id);
279 procedure Eval_Named_Integer (N : Node_Id);
280 procedure Eval_Named_Real (N : Node_Id);
281 procedure Eval_Op_Expon (N : Node_Id);
282 procedure Eval_Op_Not (N : Node_Id);
283 procedure Eval_Real_Literal (N : Node_Id);
284 procedure Eval_Relational_Op (N : Node_Id);
285 procedure Eval_Shift (N : Node_Id);
286 procedure Eval_Short_Circuit (N : Node_Id);
287 procedure Eval_Slice (N : Node_Id);
288 procedure Eval_String_Literal (N : Node_Id);
289 procedure Eval_Qualified_Expression (N : Node_Id);
290 procedure Eval_Type_Conversion (N : Node_Id);
291 procedure Eval_Unary_Op (N : Node_Id);
292 procedure Eval_Unchecked_Conversion (N : Node_Id);
294 procedure Fold_Str (N : Node_Id; Val : String_Id; Static : Boolean);
295 -- Rewrite N with a new N_String_Literal node as the result of the
296 -- compile time evaluation of the node N. Val is the resulting string
297 -- value from the folding operation. The Is_Static_Expression flag is
298 -- set in the result node. The result is fully analyzed and resolved.
299 -- Static indicates whether the result should be considered static or
300 -- not (True = consider static). The point here is that normally all
301 -- string literals are static, but if this was the result of some
302 -- sequence of evaluation where values were known at compile time
303 -- but not static, then the result is not static.
305 procedure Fold_Uint (N : Node_Id; Val : Uint; Static : Boolean);
306 -- Rewrite N with a (N_Integer_Literal, N_Identifier, N_Character_Literal)
307 -- node as the result of the compile time evaluation of the node N. Val
308 -- is the result in the integer case and is the position of the literal
309 -- in the literals list for the enumeration case. Is_Static_Expression
310 -- is set True in the result node. The result is fully analyzed/resolved.
311 -- Static indicates whether the result should be considered static or
312 -- not (True = consider static). The point here is that normally all
313 -- string literals are static, but if this was the result of some
314 -- sequence of evaluation where values were known at compile time
315 -- but not static, then the result is not static.
317 procedure Fold_Ureal (N : Node_Id; Val : Ureal; Static : Boolean);
318 -- Rewrite N with a new N_Real_Literal node as the result of the compile
319 -- time evaluation of the node N. Val is the resulting real value from
320 -- the folding operation. The Is_Static_Expression flag is set in the
321 -- result node. The result is fully analyzed and result. Static
322 -- indicates whether the result should be considered static or not
323 -- (True = consider static). The point here is that normally all
324 -- string literals are static, but if this was the result of some
325 -- sequence of evaluation where values were known at compile time
326 -- but not static, then the result is not static.
331 Fixed_Int : Boolean := False;
332 Int_Real : Boolean := False)
334 -- Returns True if it can be guaranteed at compile time that expression
335 -- N is known to be in range of the subtype Typ. If the values of N or
336 -- of either bouds of Type are unknown at compile time, False will
337 -- always be returned. A result of False does not mean that the
338 -- expression is out of range, merely that it cannot be determined at
339 -- compile time that it is in range. If Typ is a floating point type or
340 -- Int_Real is set, any integer value is treated as though it was a real
341 -- value (i.e. the underlying real value is used). In this case we use
342 -- the corresponding real value, both for the bounds of Typ, and for the
343 -- value of the expression N. If Typ is a fixed type or a discrete type
344 -- and Int_Real is False but flag Fixed_Int is True then any fixed-point
345 -- value is treated as though it was a discrete value (i.e. the
346 -- underlying integer value is used). In this case we use the
347 -- corresponding integer value, both for the bounds of Typ, and for the
348 -- value of the expression N. If Typ is a discret type and Fixed_Int as
349 -- well as Int_Real are false, intere values are used throughout.
351 function Is_Out_Of_Range
354 Fixed_Int : Boolean := False;
355 Int_Real : Boolean := False)
357 -- Returns True if it can be guaranteed at compile time that expression
358 -- N is known to be out of range of the subtype Typ. True is returned
359 -- if Typ is a scalar type, at least one of whose bounds is known at
360 -- compile time, and N is a compile time known expression which can be
361 -- determined to be outside a compile_time known bound of Typ. A result
362 -- of False does not mean that the expression is in range, merely that
363 -- it cannot be determined at compile time that it is out of range. Flags
364 -- Int_Real and Fixed_Int are used as in routine Is_In_Range above.
366 function In_Subrange_Of
369 Fixed_Int : Boolean := False)
371 -- Returns True if it can be guaranteed at compile time that the range
372 -- of values for scalar type T1 are always in the range of scalar type
373 -- T2. A result of False does not mean that T1 is not in T2's subrange,
374 -- only that it cannot be determined at compile time. Flag Fixed_Int is
375 -- used as in routine Is_In_Range above.
377 function Is_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean;
378 -- Returns True if it can guarantee that Lo .. Hi is a null range.
379 -- If it cannot (because the value of Lo or Hi is not known at compile
380 -- time) then it returns False.
382 function Not_Null_Range (Lo : Node_Id; Hi : Node_Id) return Boolean;
383 -- Returns True if it can guarantee that Lo .. Hi is not a null range.
384 -- If it cannot (because the value of Lo or Hi is not known at compile
385 -- time) then it returns False.
387 procedure Why_Not_Static (Expr : Node_Id);
388 -- This procedure may be called after generating an error message that
389 -- complains that something is non-static. If it finds good reasons,
390 -- it generates one or more error messages pointing the appropriate
391 -- offending component of the expression. If no good reasons can be
392 -- figured out, then no messages are generated. The expectation here
393 -- is that the caller has already issued a message complaining that
394 -- the expression is non-static. Note that this message should be
395 -- placed using Error_Msg_F or Error_Msg_FE, so that it will sort
396 -- before any messages placed by this call. Note that it is fine to
397 -- call Why_Not_Static with something that is not an expression, and
398 -- usually this has no effect, but in some cases (N_Parameter_Association
399 -- or N_Range), it makes sense for the internal recursive calls.
401 procedure Initialize;
402 -- Initializes the internal data structures. Must be called before
403 -- each separate main program unit (e.g. in a GNSA/ASIS context).
406 -- The Eval routines are all marked inline, since they are called once
408 pragma Inline (Eval_Actual);
409 pragma Inline (Eval_Allocator);
410 pragma Inline (Eval_Character_Literal);
411 pragma Inline (Eval_Conditional_Expression);
412 pragma Inline (Eval_Indexed_Component);
413 pragma Inline (Eval_Integer_Literal);
414 pragma Inline (Eval_Named_Integer);
415 pragma Inline (Eval_Named_Real);
416 pragma Inline (Eval_Real_Literal);
417 pragma Inline (Eval_Shift);
418 pragma Inline (Eval_Slice);
419 pragma Inline (Eval_String_Literal);
420 pragma Inline (Eval_Unchecked_Conversion);
422 pragma Inline (Is_OK_Static_Expression);